Hi Marcus, You're right about the RTL sample rate, but I'm curious about why it is so small. Is it the bus speed? The ADC is obviously fast enough for DVB-T2.
Regards, Adrian On August 24, 2018 7:42:17 PM UTC, "Müller, Marcus (CEL)" <muel...@kit.edu> wrote: >Hi Martin, > >internally, the RTL dongles are fast enough to capture full DVB-T (not >-T2) channels, and demodulate, and decode them, and deliver the video >stream to the host. However, RTL-SDR can't use that mode - it uses a >"bypass the whole Digital TV specific stuff" mode and directly passes >IQ samples through USB. > >In that mode, it simply can't do more than 2 or 3 MS/s (can't >remember), which isn't enough to cover 6 MHz - so everyone's right, you >can basically receive the AM black/white info at a partial bandwidth of >the ca 5 MHz of the luma signal, but you won't get any color >information that way, or audio with the same receiver as you do video. > >Cheers, >Marcus > >On Fri, 2018-08-24 at 12:22 -0500, Martin McCormick wrote: >> First, I will talk about the things I know for sure. The >> NTSC analog system as well as Pal systems in a lot of the rest of >> the world had a lot in common with eachother. Both systems >> transmitted an AM video signal in Vestigial single sideband mode >> such that the carrier frequency was always about 1.25 MHZ above >> the start of a channel. NTSC systems in the Americas also >> transmitted an audio carrier in FM which was always 4.9 MHZ above >> the video carrier. Pal systems used exactly the same type of >> transmissions except that the 625-line video at 25 frames per >> second made a slightly wider spectrum such that the audio and >> video carriers were separated by 5.x MHZ, making each Pal channel >> 7 or 8 MHZ wide. >> >> As others have suggested, you could probably get a >> monochrome fuzzy image if you can get your sound card to sample >> fast enough. You can also decode the mono sound by setting your >> RTL receiver to behave just like a FM broadcast receiver but set >> the frequency to whatever the video carrier frequency is plus 4.5 >> MHZ. if the video carrier is 55.250 MHZ, the audio will be at >> 59.75 MHZ. The deviation is 75 KHZ unlike FM radio which is 150 >> KHZ. >> >> That would be a good simple test to see if you are >> receiving the channel at all. >> >> I am guessing that since the RTL chips were designed for >> the European television market for cable and over-the-air >> broadcasts, they can be sampled extremely fast since the digital >> channels still take up the same bandwidth as their analog >> ancestors. >> >> Martin McCormick WB5AGZ >> >> Anders Hammarquist <i...@openend.se> writes: >> > In a message of Fri, 24 Aug 2018 10:27:40 +0200, "Ralph A. Schmid, >> > dk5ras" writes: >> > > > Hi Andres, >> > > > >> > > > just had a short look: doesn't NTSC use a nearly 6 MHz >> > > > bandwidth? >> > > > >> > > > Best regards, >> > > > Marcus >> > > >> > > Yes, no way with the RTL to catch NTSC, it does in SDR mode only >> > > 2.smth >> > >> > MHz bandwidth. >> > >> > Actually, you should be able to get a picture. The horizontal >> > resolution >> > will be >> > about half of what it would be for the full bandwidth, and no >> > colour (as >> > the colour >> > subcarrier at 3.58 MHz is outside the pass band). You want the pass >> > band >> > of the reciever >> > from just below the video carrier and as high as it will go. >> > >> > /Anders >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >_______________________________________________ >Discuss-gnuradio mailing list >Discuss-gnuradio@gnu.org >https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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